On 05/31/2016 10:29 PM, Alex Williamson wrote: > On Tue, 31 May 2016 10:29:10 +0800 > Jike Song <jike.song@xxxxxxxxx> wrote: > >> On 05/28/2016 10:56 PM, Alex Williamson wrote: >>> On Fri, 27 May 2016 22:43:54 +0000 >>> "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote: >>> >>>> >>>> My impression was that you don't like hypervisor specific thing in VFIO, >>>> which makes it a bit tricky to accomplish those tasks in kernel. If we >>>> can add Xen specific logic directly in VFIO (like vfio-iommu-xen you >>>> mentioned), the whole thing would be easier. >>> >>> If vfio is hosted in dom0, then Xen is the platform and we need to >>> interact with the hypervisor to manage the iommu. That said, there are >>> aspects of vfio that do not seem to map well to a hypervisor managed >>> iommu or a Xen-like hypervisor. For instance, how does dom0 manage >>> iommu groups and what's the distinction of using vfio to manage a >>> userspace driver in dom0 versus managing a device for another domain. >>> In the case of kvm, vfio has no dependency on kvm, there is some minor >>> interaction, but we're not running on kvm and it's not appropriate to >>> use vfio as a gateway to interact with a hypervisor that may or may not >>> exist. Thanks, >> >> Hi Alex, >> >> Beyond iommu, there are other aspects vfio need to interact with Xen? >> e.g. to pass-through MMIO, one have to call hypercalls to establish EPT >> mappings. > > If it's part of running on a Xen platform and not trying to interact > with a VM in ways that are out of scope for vfio, I might be open to > it, I'd need to see a proposal. This also goes back to my question of > how does vfio know whether it's configuring a device for a guest driver > or a guest VM, with kvm these are one and the same. Thanks, Yes, this brings us back to Kevin suggestion, > I'm not sure whether VFIO can support this usage today. It is somehow > similar to channel io passthru in s390, where we also rely on Qemu to > mediate ccw commands to ensure isolation. Maybe just some slight > extension is required (e.g. not assume some API must be invoked). Of > course Qemu side vfio code also need some change. If this can work, > at least we can first put it as the enumeration interface for mediated > device in Xen. In the future it may be extended to cover normal Xen > PCI assignment as well instead of using sysfs to read PCI resource > today. > > If above works, then we have a sound plan to enable mediated devices > based on VFIO first for KVM, and then extend to Xen with reasonable > effort. We'll work on the proposal, thanks! -- Thanks, Jike -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
